This invention relates to a device to measure angular acceleration about a predefined axis, the device being of the type having a weight and a stress transducer which are integrally fixed to a base member.
Angular velocity and angular acceleration sensors using gyroscopes are well known. However, for economical or other reasons the use of a gyroscopic instrument is not always favorable.
A recently developed device to measure angular velocity utilizes a vibratile metal bar instead of a spinning mass in a gyroscope. FIG. 1 of the accompanying drawings shows the principle of such a vibratory device. Use is made of a cross-sectionally rectangular bar 10 of a metal which is small in the expansion coefficient. On one side face, a piezoelectric element 12 for the exciting purpose is attached to the metal bar 10 with an adhesive. On the adjacent side face of the metal bar 10, another piezoelectric element 14 for the pick-up purpose is attached with an adhesive. The metal bar 10 is supported at two fulcrums 16 and 18 so that the first mode of vibration may be excited. The piezoelectric element 12 is excited by an oscillator 20 to keep the metal bar 10 vibrating in the X-Z plane. If angular velocity .OMEGA. about the axis Z is imparted to the vibrating metal bar 10, the Coriolis force acts on the vibrating portion of the bar 10 to result in excitation of vibration in the Y-Z plane, which is sensed by the piezoelectric element 14. Via an amplifier 22 the output of the piezoelectric element 14 is input to a phase detector 24, which performs phase discrimination by using the output of the oscillator 20 to thereby produce an output P representative of the angular velocity .OMEGA.. The direction of the angular velocity .OMEGA. can be identified from the phase of the output P, and the magnitude of the angular velocity .OMEGA. can be known from the amplitude of the output P.
This vibratory device is simple in construction and will be high in reliability. However, this device suffers from low resolution because angular velocity about the axis Z does not smoothly transmit to the metal bar 10 which is supported at the nodes of vibration so as to freely vibrate. Furthermore, the supporting mechanism is not sufficiently resistant to shocks.